The present invention relates generally to a method and apparatus for controlling an injector in a diesel engine exhaust aftertreatment system and, more particularly, to a method and apparatus that compensates for deviations from expected performance of the injector.
In diesel engines, it is typical to use a diesel particulate filter DPF downstream of the engine to filter particulates from the engine exhaust. If too much soot collects on the DPF, the soot can burn in an uncontrolled manner and may crack or melt the DPF. This phenomenon is sometimes referred to as so-called “runaway” or uncontrolled regeneration. To avoid problems such as runaway regeneration, it is common to periodically inject fuel via a so-called “seventh injector” into the exhaust pipe to burn off the soot. Over time, the seventh injector tends to get plugged by soot (particular matter). Fuel pressure may also vary due to fuel supply system degradation over time such as when the fuel filter gets plugged. There may also exist variations in flow capacity from engine to engine due to manufacturing variabilities. It is desirable to compensate for these phenomena to ensure proper control of temperature in the exhaust stream to burn off the soot on the DPF in a controlled manner that does not damage the DPF. Similar problems associated with clogging of injectors are true for other injectors in the diesel exhaust aftertreatment system, such as urea injectors for selective catalytic reduction devices, and it is similarly desirable to compensate for clogging in these systems.
According to an aspect of the present invention, a method for controlling injection of a substance in a diesel engine exhaust aftertreatment system comprises generating a feedforward signal as a function of a desired output signal, the desired output signal corresponding to an output sought to be achieved through injection of the substance, measuring actual system output and generating an actual output signal corresponding to an output actually achieved through injection of the substance, comparing the desired output signal and the actual output signal and generating an error signal corresponding to a difference between the desired output signal and the actual output signal, generating a control signal as a function of the error signal and the feedforward signal for controlling an amount of the substance to inject, and adjusting the feedforward signal by an adaptive factor, the adaptive factor being a function of the error signal.
According to another aspect of the present invention, a diesel engine with an exhaust aftertreatment system comprises at least one injector device for injecting a substance into an exhaust stream, at least one sensor for measuring an actual system output resulting from injection of the substance and generating an actual output signal, a controller arranged to compare a desired output signal, the desired output signal corresponding to an output sought to be achieved through injection of the substance, and the actual output signal, the actual output signal corresponding to an output actually achieved through injection of the substance, and generate an error signal corresponding to a difference between the desired output signal and the actual output signal, the controller being arranged to generate a feedforward signal in response to the desired output signal, the controller being arranged to generate a control signal as a function of the feedforward signal and the error signal for controlling an amount of the substance to inject, and the controller being arranged to adjust the feedforward signal by an adaptive factor, the adaptive factor being a function of the error signal.